Processes for producing recombinant organisms are known. They typically involve transformation of an organism with an exogenous nucleic acid vector, which may integrate with the host genome or remain in a stable independent (for example, extra-chromosomal) state.
Integration of an exogenous nucleic acid into the host genome involves a double-crossover event between the vector and an endogenous nucleic acid. Double-crossover recombination happens at frequencies which are too low to reliably identify integrants by chance alone. Therefore, a means to select for one or both crossovers has a huge benefit on the frequency of identification in both time and labour.
Selection markers of use in screening for recombination events are known. Such markers are typically protein coding sequences that confer a selective advantage (positive-selection) or disadvantage (counter-selection) to a host organism. A number of positive-selection and counter-selection markers are known and can be of use in screening for organisms in which a desired recombination event has occurred. A positive-selection marker typically comprises a gene that when expressed allows an organism to survive in a particular growth environment. A counter-selection marker typically comprises a gene that when expressed produces a toxin which is lethal to an organism.
In bacteria other than Clostridia, there is a plethora of counter-selection markers available but unfortunately either due to physiological or genetic reasons, the vast majority do not work in Clostridia.
It is an object of the invention to overcome one or more of the disadvantages of the prior art, or to at least to provide the public with a useful choice.